This invention relates generally to heat pump systems and, more particularly, to a method and apparatus for controlling the pressure within the interconnecting tubing and other refrigerant containing components thereof so as to prevent the exceeding of the maximum design pressure when using a high pressure refrigerant.
The refrigerant which has been commonly used in conventional residential and commercial air conditioners and heat pumps has been R-22, an HCFC refrigerant. However, because of the recent concern about environmental effects, the CFC and HCFC refrigerants are being phased out. Non-chlorinated refrigerants that are being developed as replacements in the residential and light commercial systems, tend to be of higher pressure than the R-22. One of the more promising replacement refrigerants is HFC R-410A, with operating pressures up to 70% higher than R-22.
Use of higher pressure refrigerants has the greatest impact on the high pressure side of a system. Accordingly, for an air conditioner, the outdoor unit needs to be substantially changed in design in order to accommodate these higher pressures. That is, to meet safety agencies and organization requirements, most refrigerant containing components on the high pressure side of the system must be designed to withstand the significantly higher pressures. The low pressure side components, on the other hand, may be used with minor modifications and/or precautions. The costs associated with these changes of both the outdoor and indoor sections to accommodate an R-410A refrigerant is not significantly more than that for replacing an R-22 air conditioner with a new R-22 air conditioner and is therefore economically feasible. This is not necessarily so in the case of a heat pump.
To accommodate an R-410A heat pump operating in the cooling mode, the outdoor section must be redesigned to accommodate the higher pressures as discussed hereinabove. In addition, to accommodate the heating mode of operation, wherein the high pressure section is in the indoor coil, the indoor refrigerant containing components, as well as other components in the outdoor unit, must be redesigned.
In addition to the outdoor and indoor coils, there is a portion of the system known as the "line set". This is the interconnecting tubing which connects the indoor and outdoor sections of air conditioners and heat pumps. Typically, R-22 air conditioners and heat pumps have used what is referred to as RST (Refrigerant Service Tube) refrigeration copper tubing for line sets. The physical dimensions of RST tubing is not regulated or recognized by any safety organization or national standards but is simply the general air conditioning and refrigerant industry accepted tubing.
The line set is typically considered field fabricated and is generally regulated by local building codes. Most local and national codes for refrigerant piping reference the ASME standard, ASME B31.5 "Refrigeration Piping". For R-410A air conditioners and R-410 A heat pumps operating in the cooling mode, the standard RST tubing meets the requirements set forth in the ASME B31.5. However, with heat pumps, the conventional R-22 construction of the line set vapor line typically does not meet the requirement of the ASME B31.5 standards. That is, the standard RST vapor tube installed in a heat pump will have a rated working pressure below that of the ASME B31.5 standard when using R-410 A as a refrigerant.
One approach to accommodating the R-410A refrigerant is to change the line sets or at least the vapor line. However, this causes disproportionate costs to be incurred. First of all, the line sets of existing systems are often located in the walls between the outdoor and indoor systems and cannot be easily accessed. Secondly, aside from the labor costs, the costs of copper tubing is expensive because (a) thicker walls require more copper and (b) the low volume of thicker walled copper tubes drives the costs up disproportionately. For these reasons, the required changes that need to be made to an R-22 heat pump to accommodate the use of R-410A are significantly higher than the costs to replace the R-22 with a new R-22 system and is therefore not economically feasible.
It is therefore an object of the present invention to provide an improved method and apparatus for accommodating the use of a higher pressure refrigerant in a system designed for use of a lower pressure refrigerant.
Another object of the present invention is the provision for not exceeding the maximum design pressure when using high pressure refrigerant in a heat pump system.
Yet another object of the invention is the provision for converting a low pressure refrigerant system to a high pressure refrigerant system in an economical and effective manner.
These objects and other features and advantages become readily apparent upon reference to the following description when taken in conjunction with the appended drawings.